Linear compressor

ABSTRACT

The invention concerns a linear compressor ( 1 ) with a piston ( 16 ) reciprocating in a cylinder ( 8 ), a linear motor acting upon the piston ( 16 ) and a resonance spring arrangement ( 5 ) connected with the piston ( 16 ). It is endeavoured to reliably avoid damaging the compressor during operation.  
     For this purpose, the resonance spring arrangement ( 5 ) has a fixed stop ( 48 ) allocated to the upper dead point of the piston ( 16 ).

The invention concerns a linear compressor with a piston reciprocating in a cylinder, a linear motor acting upon the piston and a resonance spring arrangement connected with the piston.

The linear motor of such a linear compressor has a stator and an armature moving in relation to the stator and being connected with the piston. When the armature reciprocates, the piston reciprocates accordingly, thus increasing and reducing a compression chamber in the cylinder. A resonance spring arrangement is connected with the piston or with the armature, said arrangement being adapted to the operation frequency of the linear motor. The linear motor is then operated in the resonance frequency of the spring.

With a piston operated by a rotation motor via a crankshaft, the position of the piston in the upper dead point can be determined accurately. With a linear motor this is not possible. By means of a design of the linear motor, it can be determined for each operation area, where the upper dead point of the piston approximately is, that is, the dead point at which the compression chamber in the cylinder has its smallest extension. As soon as the operation conditions change, for example the pressures in a refrigeration system, which is supplied by the linear compressor, there is a risk that the piston strikes the front side of the cylinder. As usually inlet and outlet valves are located here, such a stroke can cause substantial damage. If a security distance were used, the remaining dead space in the cylinder would be too large, which would reduce the efficiency.

A linear compressor as mentioned in the introduction is known from U.S. Pat. No. 6,783,335 B2. The resonance spring is located on the side of the armature facing away from the piston. An anti-collision device is connected with the resonance spring, said device having an elastic element and a damping element. An excessive movement of the piston will cause the middle section of the resonance spring to strike the damping element, the impact being further damped by the elastic element, which deforms elastically for the damping. However, this does not provide the opportunity of a final setting of a defined end position for the piston.

U.S. Pat. No. 6,056,519 shows a possible embodiment of a resonance spring arrangement. The resonance spring consists of a stack of several plate spring plates, each spring plate having several mutually interlocked spring arms, which are formed by slots in the plates.

U.S. Pat. No. 6,755,627 B2 shows a further linear compressor with an anti-collision device, which is located at the piston side end of the armature, between the stator and the armature. Before reaching the upper dead point of the piston, the armature strikes a spring arm and moves it until the spring arm strikes an elastic damping element. The elastic damping element is still deformable to a certain extent, however, with increased resistance. This does not either provide setting of a defined end position of the piston.

U.S. Pat. No. 6,779,984 B2 proposes a different method. Here a sensor is provided, which indicates the reaching of the upper dead point of the piston. The sensor then controls the electrical supply to the linear motor so that a striking of the piston on the front wall of the cylinder is prevented. Such a control, however, is relatively expensive.

The invention is based on the task of reliably preventing a damaging of the compressor during operation.

With a linear compressor as mentioned in the introduction, this task is solved in that the resonance spring arrangement has a fixed stop allocated to the upper dead point of the piston.

The stop thus provides a well-defined and fixed stop position for the piston in the upper dead point. When the piston is in the upper dead point, the resonance spring arrangement bears on the stop and permits no further movement. A damping element, which could be deformed when reaching the stop, is not available and not necessary either. When the spring bears on the stop, it has already been deformed. The heavier the deformation, the larger the deformation resistance. The impact of the resonance spring arrangement on the stop thus occurs in the area of a lower speed, the impact being, in fact, damped already.

Preferably, the cylinder and the stop are displaceable in relation to each other in the movement direction of the piston during the mounting of the linear compressor. This provides a simple manner of setting the dead space in the cylinder. An external force moves the piston so far that the resonance spring arrangement bears on the stop. The piston is thus in its “upper dead point”, that is, in a position, in which the compression chamber in the cylinder shall have its smallest extension. In this position, the cylinder is now displaced so far in relation to the piston that the dead space has the desired minimum volume. In this position the cylinder is then fixed, for example connected with a fixture, which again is connected with the stator of the linear motor.

Preferably, the resonance spring arrangement has at least one plate spring, which gradually comes to rest on the stop, when the piston moves in the direction of its upper dead point. Thus, a sudden impact of the resonance spring arrangement on the stop is avoided. On the contrary, the free spring length is reduced gradually with the movement of the piston towards its upper dead point, which causes that the rigidity of the resonance spring arrangement is accordingly increased. When the plate spring then rests completely on the stop, the piston has reached its upper dead point. When, during the pressure stroke of the compressor, the plate spring can successively roll on the stop, stop noises are reduced and the life of the plate spring is increased. Further, the shape, particularly the inclination, of the stop permits a very accurate setting of the characteristic of the resonance spring system. The same plate springs can also be used for different compressors. The spring properties can then be influenced via the stop.

Preferably, the stop is located in a stop housing, whose extension is adapted to the cross-section of the linear motor. In other words, the stop housing has the same outer diameter as the linear motor, deviations in both directions being possible to a certain extent, as long as the stop housing does not collide with an enclosure, in which the linear motor is adapted. Then, the space provided by the enclosure can be used to its full extent, so that the resonance spring arrangement can be relatively large.

Preferably, the plate spring has in the unloaded state a predetermined distance to the stop housing. Thus, the plate spring can initially move a distance before starting to rest on the stop.

Preferably, the stop has a convex contact surface. Thus, the total width of the spring arms of the plate spring will not come to rest on the stop surface, but only a partial area, as the stop is arched. This may prevent a possible sticking of the plate spring, which might, for example, be caused by a lubrication oil film. Further, excessive tensions in the material of the plate spring are prevented, if the impact of the plate springs on the stop housing does not occur exactly parallel to the stop surface, but with an edge. This also makes it possible to keep the noises small.

Preferably, the plate spring has at least one arched arm. Thus, a relatively long arm can be realised, that is, the length of the arm is not limited by the radius of the stop housing.

It is preferred that the plate spring has several arched arms, which are located and mutually interlocked in the form of several spirals. This provides a simple manner of preventing a tilting moment on the armature or on the piston. The spring rigidity can be increased. A sufficient length is available for all arms.

Preferably, the plate spring has an annular outer section, from which the arms extend radially inwards. The outer section can then be used for fixing the plate spring on the stop housing. The stop housing can, for example, have raised support faces, on which the plate spring bears on the housing.

It is also advantageous, when the outer section has fixing openings, slots separating adjacent arms from each other extending into an area between the fixing openings. Then, also another share of the outer section can be utilised for the length of the spring arms. At the same time, screws can be guided through the fixing openings, which then retain the spring in a correct position in relation to the stop housing. A turning of the plate spring in relation to the spring housing is thus precluded.

Preferably, the plate spring and the stop housing have an auxiliary positioning device, which ensures an allocation by angle of the plate spring and the stop housing in relation to each other. When the plate spring is made with several spiral-shaped arms, it is expedient to ensure that each arm faces a correspondingly spiral-shaped stop in the stop housing. The more accurate the allocation of stop and arm can be ensured, the more accurate is the control of the working behaviour of the linear motor.

Preferably, a central area of the plate spring has an opening, through which is guided an element connected with the piston. Thus, the arms are connected with each other in the middle through the central area. The opening is a simple opportunity of connecting the spring with the piston or with the piston via the armature, respectively.

Preferably, the stop is located on a side of the linear motor facing away from the cylinder. Here, sufficient space is available. Thus, the stop neither prevents the movement of the piston in the cylinder, nor will design measures be required to provide a space for the stop at the cylinder-side end of the linear motor.

In the following, the invention is described on the basis of a preferred embodiment in connection with the drawings, showing:

FIG. 1 a schematic longitudinal view through a linear compressor

FIG. 2 a top view of a plate spring

FIG. 3 a top view of a stop

FIG. 4 a section IV-IV according to FIG. 3

FIG. 5 a schematic view of the spring characteristic of the resonance spring

FIG. 6 a perspective view of the resonance spring arrangement

FIG. 7 the resonance spring according to FIG. 6 in a partial section.

FIG. 1 shows a linear compressor 1, which is located in a hermetically closed capsule 2.

The linear compressor 1 has a compression section 3, a driving section 4 and a resonance spring arrangement 5. The unit formed by the compression section 3, the driving section 4 and the resonance spring arrangement 5 is suspended in the capsule 2 by means of two plane annular springs 6, 7, each in the shape of a spiral with one winding. The annular springs 6, 7 are fixed on the driving section 4.

The compression section 3 has a cylinder 8, whose front side is covered by a cylinder head 9. The cylinder 8 and the cylinder head 9 are joined by a capsule 10 in the manner of a cartridge. A suction muffler 11 and a pressure muffler 12 are fixed on the cylinder head 9. The suction muffler 11 is connected with a suction opening 13 and the pressure muffler 12 is connected with a pressure opening 14 in the cylinder head.

The capsule 10 is inserted in an intermediary ring 15, which is connected with the driving section 4. During mounting, the capsule 10 and thus the cylinder 8 are displaceable in relation to the intermediary ring 15 within certain limits in the axial direction of the cylinder. When, as will be explained below, a predetermined position of the cylinder in relation to the driving section 4 has been reached, the capsule 10 is fixed in the intermediary ring 15, for example by means of welding, soldering or gluing.

In the cylinder 8 is located a piston 16, which borders a compression chamber 17 together with the cylinder 8 and the cylinder head 9.

The driving section 4 has a linear motor. The linear motor has an outer stator 18 with a recess 19 for a winding, not shown in detail, and an inner stator 20. Between the outer stator 18 and the inner stator 20 is located an annular gap 21, in which an armature 22 is movable. The armature carries permanent magnets 23, which are connected with each other by means of two rings 24, 25. The rings 24, 25 can, for example, be made of plastic. The rings 24, 25 are connected with inner rings 26, 27 via arms, not shown in detail, which are guided through slots in the inner stator 20.

The inner rings 26, 27 are connected with a piston rod 28, which again is connected with the piston 16.

The outer stator 18 and the inner stator 20 are connected with each other through motor covers 29, 30, which are mutually interlocked by means of screw bolts 31. The screw bolts are guided in parallel to the movement direction of the piston rod 28.

The intermediary ring 15 is connected with the cylinder-side motor cover 30, for example by welding, gluing or soldering. The concentric design of motor cover 30, intermediary ring 15, capsule 10 and cylinder 8 causes that the longitudinal axes of the piston rod 28 and the cylinder 8 are coincident. This reduces the frictional losses between piston and cylinder. Any small tolerance errors are equalised by a ball joint between the piston rod and the piston.

The resonance spring arrangement 5, which is located at an end of the driving section 4 opposite to the compression section 3, has a spring pack 32 of several plate springs 33. In a central area 34, the spring pack 32 is connected with the piston rod 28. An outer section 35 of the spring pack 32 is connected via bolts 36 with a stop housing 37, which forms a stop for the spring pack 32.

At the end projecting from the spring pack 32, the piston rod 28 is connected with an oil pump arrangement 38 that is immersed in an oil sump, not shown in detail, which forms in the lower part of the capsule 2.

When the winding located in the recess 19 is energised, the armature 22 moves in one direction taking along the piston rod 28 in this direction. When the direction of the current is reversed, the armature 22 with the piston rod 28 moves in the opposite direction and accordingly also moves the piston 16 in the opposite direction. This will periodically increase and reduce the volume of the compression chamber 17. The resonance spring arrangement 5 is adapted to the frequency of the current, so that the movable part of the linear compressor 1, which is formed by the armature 22, the piston rod 28, the piston 16, the oil pump arrangement 38 and the moved part of the resonance spring arrangement 5, oscillates in resonance.

FIG. 2 shows a top view of a plate spring 33 with the outer section 35 and the middle section 34. The middle section 34 has an opening 39, through which the piston rod 28 is guided. In the outer section are located several fixing openings 40, through which the bolts 36 are guided to connect the spring pack 32 with the stop housing 37.

The middle section 34 is connected with the outer section 35 via several arms 41, in the present embodiment three arms 41. These arms are located to be spiral-shaped, each spiral practically travelling an angle of 360°.

The arms 41 are surrounded by slots 42. The slots 42 extend into the outer section 35, that is, in an area between fixing openings 40.

When, now, a force acts upon the middle section 34, it is displaced in relation to the outer section 35, namely, perpendicularly to the drawing level in relation to the view in FIG. 2. This also applies, when several plate springs have been assembled to a spring pack 32. FIG. 6 shows the spring pack 32 in the deflected state.

The stop housing 37, shown in a top view in FIG. 3 and in a section in FIG. 4, firstly has threaded bores 43, which can receive the bolts 36 for fixing the spring pack 32 on the stop housing 37. The connection between the spring pack 32 and the stop housing 37 can of course also be made with other suitable means, for example, rivets. The threaded bores 43 are surrounded by a projection 44, which ensures that in the non-deflected state the spring pack 32 has a predetermined distance to the stop housing 37.

Further, the stop housing has a central opening 45, through which the piston rod 28 is guided. Finally, the stop housing 37 has two positioning bores 46, through which fitting pins, not shown in detail, can be guided, which ensure together with corresponding positioning bores 47 in the plate spring 33 that the spring pack 32 has a predetermined angle alignment to the stop housing 37.

For each arm 41, the stop housing 37 has a stop 48, which extends, in an equally spiral-shaped manner from the radial outside towards the radial inside, in the form of a continuous projection projecting from the stop housing 37 in the direction of the spring pack. As is particularly clear from FIG. 4, the stop 48 has a convex rounded surface, on which the arms 41 will rest in turn. Thus, it is avoided that an arm 41 resting on the stop 48 gets stuck because of an oil film or comes to rest on the stop with an edge. On the contrary, each arm 41 will always only rest on a part of the surface of the arched stop 48.

The stops 48 are adapted to the arms 41, or rather to the deformation behaviour of the arms 41, in such a manner that during a displacement of the middle section 34 in the direction of the stop housing 37, the arms 41 will eventually come to rest on the stops 48. Thus, the stop face of the arms 41 on the stops 48 increases with an increasing stroke of the middle section 34. The exact course of the stops 48 can be found by simple calculations or tests. For example, the inclination of the stops 48 from the outside to the inside can be changed.

The increasing support of the arms 41 on the stops 48 reduces the free section of the arms 41, and thus the section being available for resilient properties. Accordingly, the spring pack 32 will become more and more rigid, the more the spring pack 32 approaches the stop housing 37. This course is shown in FIG. 5. Here a force F, which is required for the deformation, is shown via a displacement X of the middle section 34 in relation to the outer section 35. It can be seen that in a contact point P also an increase of the force will not effect a further displacement of the middle section 34. In this case, the middle section 34 of the spring pack 32 will namely rest completely on the stops 48.

It can be seen that the stopping of the piston movement does not occur abruptly, but the piston 16 is braked by a continuously increasing braking force. This gives a quiet operation with little wear.

For the mounting, the spring pack 32, which is already connected with the piston 16 via the piston rod 28, can be brought to rest on the stop housing 37. This position corresponds to the upper dead point of the piston 16. The cylinder 8 with its capsule 10 is then displaced so far into the intermediary ring 15 that the compression chamber assumes its minimum volume. Accordingly, the minimum distance exists between the piston 16 and the cylinder head 9. In this position, the capsule 10 is then connected to the intermediary ring 15.

Multiple deviations from the embodiment shown can be imagined. In stead of a resonance spring arrangement 5, which merely has plate springs 33, also a combination of at least one plate spring 33, which can be moved up to the stop housing 37, and a helical or spiral spring can be used. In any case, it must be ensured, however, that the resonance spring arrangement 5 absolutely limits the movement of the piston 16. 

1. Linear compressor with a piston reciprocating in a cylinder, a linear motor acting upon the piston and a resonance spring arrangement connected with the piston, characterised in that the resonance spring arrangement (5) has a fixed stop (48) allocated to the upper dead point of the piston (16).
 2. Linear compressor according to claim 1, characterised in that the cylinder (8) and the stop (48) are displaceable in relation to each other in the movement direction of the piston (16) during the mounting of the linear compressor (1).
 3. Linear compressor according to claim 1 or 2, characterised in that the resonance spring arrangement (5) has at least one plate spring (33), which gradually comes to rest on the stop (48), when the piston (16) moves in the direction of its upper dead point.
 4. Linear compressor according to one of the claims 1 to 3, characterised in that the stop is located in a stop housing, whose extension is adapted to the cross-section of the linear motor.
 5. Linear compressor according to claim 4, characterised in that the plate spring (33) has in the unloaded state a predetermined distance to the stop housing (37).
 6. Linear compressor according to one of the claims 1 to 5, characterised in that the stop (48) has a convex contact surface.
 7. Linear compressor according to one of the claims 3 to 6, characterised in that the plate spring (33) has at least one arched arm (41).
 8. Linear compressor according to claim 7, characterised in that the plate spring (33) has several arched arms (41), which are located and mutually interlocked in the form of several spirals.
 9. Linear compressor according to claim 7 or 8, characterised in that the plate spring (33) has an annular outer section (35), from which the arms (41) extend radially inwards.
 10. Linear compressor according to claim 9, characterised in that the outer section (35) has fixing openings (40), slots (42) separating adjacent arms (41) from each other extending into an area between the fixing openings (40).
 11. Linear compressor according to one of the claims 3 to 10, characterised in that the plate spring (33) and the stop housing (37) have an auxiliary positioning device (46, 47), which ensures an allocation by angle of the plate spring (33) and the stop housing (37) in relation to each other.
 12. Linear compressor according to one of the claims 3 to 11, characterised in that a central area (34) of the plate spring (33) has an opening (39), through which is guided an element (28) connected with the piston (16).
 13. Linear compressor according to one of the claims 1 to 12, characterised in that the stop (48) is located on a side of the linear motor facing away from the cylinder (8). 